Unsaturated olefins, aromatics, and minor amounts of sulfur-containing compounds in a lubricant base oil tend to form gums by reacting with oxygen, and finally to form carbon deposits, especially at critical locations like inlet valves, pistons, oil pans and the combustion chamber, which will facilitate formation of engine deposits and seriously affect the performance of the engine, causing engine problems like difficult starting, idle instability, poor driving, poor acceleration, and severe power loss. Carbon deposits hinder the rotation of transmission gears, worsen gear wear and shorten the gearbox life, resulting in unnecessary expensive maintenance cost. By adding a cleansing and dispersing agent to a lubricant base oil as the lubricating oil additive, the prior art has developed a lubricating oil composition exhibiting cleansing performance (i.e. deposit formation suppressing performance). With this lubricating oil composition having cleansing performance, coking and carbon depositing on the top of pistons can be effectively reduced, which helps to reduce valve system, engine parts and gear wear, and finally elongate the safe operation cycle of engines and gears and the service life of spare parts.
U.S. Pat. No. 5,725,612 discloses a Mannich base and a process for producing same. The Mannich base is produced by reacting a hydrocarbyl-substituted alkyl o-cresol with an aldehyde and an amine, and after produced into a cleansing agent, exhibits some deposit formation suppressing performance.
US 20040168364 discloses a Mannich base and a process for producing same. The Mannich base is produced by the reaction of a phenolic compound with an aldehyde and an amine, and after produced into a cleansing agent, exhibits some deposit formation suppressing performance.
In recent years, the product specification of gasoline engine oils has been gradually upgraded from SJ/GF-2 to SL/GF-3, SM/GF-4 and SN/GF-5. The dispersing and cleansing performance of engine oils has been always identified as one of the critical indexes of the product specification. According to the recent SN/GF-5 specification in 2010, more stringent requirements have been raised on the piston cleansing ability of engine oils in the IIIG engine test, with the pass criteria in a piston deposit rating upgraded from 3.5 to 4, which represents a significant increase. Further, more stringent requirements have been raised on the engine sludge rating in the VG engine test evaluation, with less amount of sludge under more severe working conditions. All of these laid more and more stringent requirements on the cleansing and dispersing agent in lubricating oils. In addition, the product specification and grade of diesel engine oils have been changing as the diesel engine structure or operating conditions change, and further in response to the energy-saving and emission-reduction requirement, resulting in frequently upgrading of diesel engine oils. The product specification of diesel engine oils has been gradually upgraded from CF-4 to CH-4, CI-4 and most recently CJ-4. The application of the EGR exhaust gas recirculation system to the diesel engine decreases NOx emission, however, brings about the problem of increasing soot in lubricating oils. In use, carbon black in the diesel engine oil has been increased from a content of 2% according to the CF-4 specification gradually to 6.7% according to the CJ-4 specification. This will raise more and more stringent requirements on the piston cleansing performance and the soot dispersing performance of oil products.
However, the lubricating oil composition with the prior art cleansing and dispersing agent is insufficient in meeting the requirements set by such lubricating oil products of upgraded specification.
In addition to the adverse effects of deposit, rust on engines and gears will seriously shorten the service life of engine and gearbox, and that on some key parts will largely affect the operating performance of engine and gear box. The prior art pays a lot of attention on the cleansing performance of the lubricating oil composition, but little on the anticorrosion performance thereof.
Therefore, there is still a need for a lubricating oil composition, which not only meets today's higher and higher requirements on the cleansing and dispersing performance set by lubricating oil products of upgraded specification, and also shows excellent anticorrosion performance.